Scratch any new US weapon today and just below the surface you're apt to find an out-of-the-way mapmaker. Indeed, the current evolution in America's military modernization - and whether the new armaments work - relies on a little-known organization tucked up near the Naval Observatory.
The Defense Mapping Agency (DMA), the Pentagon's ''AAA,'' still puts out 30 million to 40 million paper maps a year. Central America is much in demand these days. But the age of computers has turned the military's map shop from a place of green eyeshades into a highly sophisticated outfit working in centimeters instead of kilometers, nanoseconds instead of hours and minutes, 256-color digitized displays instead of pen and ink.
The DMA's director, Rear Adm. E.A. Wilkinson Jr., likes to point out that his organization is ''in the humanitarian business as well as the weapons business, '' helping in search-and-rescue efforts and providing navigation aids to mariners and aviators. Geodetic data gathered and analyzed from DMA's 50 posts around the world also have great commercial application - helping locate natural resources, for example.
But it is the controversial new high-tech thrust in finding and destroying military targets with great precision over long distances that takes most of DMA's effort.
The new ballistic missiles (MX and Trident) are strongly affected by gravity as they arc thousands of miles. Using data from satellites and from instruments on the ground, DMA employees (most of whom are civilians) are measuring gravity at millions of spots on Earth. This information will be plugged into missile targeting and flight-path computers.
The Pershing II intermediate-range nuclear missile finds its target with an on-board radar system that compares the flight path with radar-reference scenes stored in cassettes, shipped to the field for preplanned targets and inserted just before launch by on-site commanders.
Cruise missiles use radar altimeters at low level to compare the terrain with precise digitized maps stored in the missile's computer. This Tercom system (terrain contour matching) tells the missile to correct its course if necessary. Recently, serious questions have been raised about whether Tercom will work as advertised.
But Admiral Wilkinson says he has faith in the system. ''I'll tell you someone who seems to think it's going to work pretty good, and that's the Soviets,'' he says. ''They obviously are quite worried about the Pershing II and the cruise missile.''
New ways of mapping are very important to the more traditional missions of soldier and airman as well. Fresh information on slopes, soil types, foliage, and man-made features like bridges, roads, and dams are indispensable to infantry commanders making ''go-no go'' decisions. DMA officials won't say much about it, but they also work on things like whether a certain bridge in Poland will support an M-1 tank.
Most jet cockpits now have strip maps that automatically unroll under the direction of doppler radar. ''Separate a guy from his moving map display, and you might as well cut off his arm today,'' says the DMA's deputy director, Brig. Gen. William B. Webb, an Air Force pilot. Paper maps are being replaced with 35 -millimeter film strips. Eventually these will be digitized, stored on computer tape, and displayed like a video game.
Admiral Wilkinson reminds a visitor that much of the earth remains inadequately mapped, that in many places ''we're still using soundings that Captain Cook got back centuries ago.''
So far, DMA has digitized (transferred topography and man-made features to computer tape) about one-third of the earth's 39 million square nautical miles. Using satellites, stereo photography, and doppler ground stations, it can fix individual spots to within one meter, vertically as well as horizontally. Just over the agency's technological horizon is the use of artificial intelligence to produce maps more precisely and much quicker.
''We're going to be able to describe the surface of the earth in ways that we can't even begin to describe it today,'' Wilkinson says. ''And when we do, that's going to have all sorts of military and commercial applications.''